Secondary cancers which are related with treatment of childhood acute lymphoblastic leukemia (ALL) is a significant problem with longer term. For development of secondary cancer after treatment, the latency period varies between 5 and 10 years. In this case, a 13 year-old-boy diagnosed as high-risk ALL was treated with chemotherapy and prophylactic cranial radiotherapy at a dose of 1800 cGy. Six years after the end of treatment he developed a 5×5×4 cm mass at the right temporal region of the cranium. The mass was excised totally with clear surgical margin. Pathology of mass has been diagnosed as malignant fibrous histiocytoma (MFH), recently referred to as an undifferentiated pleomorphic sarcoma (UPS). After treatment of childhood ALL, reported cases of secondary MFH is extremely rare in the literature. Herein we present a case of MFH/UPS that developed as a secondary cancer 6 years after the end of ALL treatment.